The present invention concerns a method for the reduction of a feedstock comprising a metal compound or compounds, such as a metal oxide, to form a reduced product. As is known from the prior art, electrolytic processes may be used, for example, to reduce metal compounds or semi-metal compounds to metals, semi-metals, or partially reduced compounds, or to reduce mixtures of metal compounds to form alloys. In order to avoid repetition, the term metal will be used in this document to encompass all such products, such as metals, semi-metals, alloys, intermetallics, and partially reduced products.
In recent years, there has been great interest in the direct production of metal by direct reduction of a solid feedstock, for example, a metal-oxide feedstock. One such direct reduction process is the Cambridge FFC® electro-decomposition process (as described in WO 99/64638). In the FFC process, a solid compound, for example a metal oxide, is arranged in contact with a cathode in an electrolysis cell comprising a fused salt. A potential is applied between the cathode and an anode of the cell such that the compound is reduced. In the FFC process, the potential that produces the solid compound is lower than a deposition potential for a cation from the fused salt.
Other reduction processes for reducing feedstock in the form of a cathodically connected solid metal compound have been proposed, such as the Polar® process described in WO 03/076690 and the process described in WO 03/048399.
Conventional implementations of the FFC process and other solid-state electrolytic reduction processes typically involve the production of a feedstock in the form of a porous preform or precursor, fabricated from a sintered powder of the solid compound to be reduced. This porous preform is then painstakingly coupled to a cathode to enable the reduction to take place. Once a number of preforms have been coupled to the cathode, then the cathode can be lowered into the molten salt and the preforms can be reduced. During reduction of many metal oxides, for example titanium dioxide, the individual particles making up the preform undergo further sintering forming a solid mass of metal, which may have entrapped salt.
It may sometimes be desirable to produce metallic powder, for example powder for subsequent processing using various known powder metallurgy techniques. Powder has previously been produced by a processing route involving direct reduction of solid preforms, such as pellets, to form solid pellets of reduced metal. After reduction, these reduced pellets may be crushed or ground to form powder of a desired particle size. Some metals such as titanium are difficult to comminute to powder without undergoing additional steps such as hydrogen deprecation.